Rotary pumps have used journal bearings to stabilise a spinning rotor or impeller. It has been noted that commonly the impeller rotates about a central axis within the pump housing and may whirl to the side of the housing when the impeller is rotated at high speeds with insufficient load and results in instability in relation to the rotation of the impeller.
The impeller of the rotary blood pump disclosed within U.S. Pat. No. 6.227,797—Watterson et al. is hydrodynamically suspended and may under certain conditions the impeller or rotor may experience a touchdown event. A touchdown event is a situation where the impeller or rotor touches or contacts the inner walls of the pump housing. Touchdown of the impeller or rotor often leads to damaging the impeller, housing and/or the pumping fluid. If a touchdown event occurs in a rotary blood pump implanted in a patient such an event may result in impaired pump performance that may result in complications for the patient. Touchdown may be avoided by increasing the stability of the impeller or rotor or increasing the stiffness and/or dampening of the impeller or rotor.
U.S. Pat. No. 5,324,177—Golding et at describes a means for increasing impeller or rotor stability in a rotary pump. The impeller and/or rotor are biased by a load provided by additional load acting only in radial orientation in respect of the axis of rotation of the pump. This has the effect of offsetting the rotor and thus stabilising the rotor in only the radial direction. The arrangement disclosed in U.S. Pat. No. 5,324,177, may also tend to destabilise the impeller in relation to the axial positioning of the impeller. Additionally, the radial biasing of the impeller is only useful in situations where the motor stators of the pump are positioned radially in respect of the axis of rotation of the impeller. This may lead to a considerably increase in size of the overall pump.
The present invention aims to at least address or ameliorate one or more of the above disadvantages associated with the abovementioned prior art.